Ignition system



Aug- 25, 1959 D. E. sUNsTElN IGNITION SYSTEM Filed Jan. 24, 1956 fill'vl wr 0 cJ 7 NN 7 my a WJ 5 u W m m United States Parent() IGNITIONSYSTEM David E. Sunstein, Bala-Cynwyd, Pa., assigner to PhilcoCorporation, Philadelphia, Pa., a corporation of Penn- SylvaniaApplication January 24, 1956, Serial No. 560,976

2 Claims. (Cl. S15- 200) This invention relates to ignition systems, andwhile the invention is applicable particularly to ignition systems forautomobles, it is intended to be employed wherever it may find usefulapplication.

Due to the fact that most of the present day automobile engines haveeight-cylinder engines with high compression ratios frequently in excessof 7.5 to 1, a problem has arisen with respect to the stringent ignitionrequirements of such engines. Optimum perforance cf such engines can beattained only by supplying to the spark plugs an extremely high voltagegreatly in excess of that which was suitable for prior engines havinglower compression ratios. The reason for this is that with highercornpression ratios, the breakdown strength of the gasoline mixture isincreased. Moreover, greater engine eflciency through use of leanermixtures can be achieved if the spark plug gap is increased to giveoptimum performance, and this also leads to the need for even highervoltage. The spark-creating voltage must be maintained high to assurereliable firing of the spark plugs even when the plugs are fouled to aconsiderable degree, e.g. to a resistance of 100,000 ohms, which canresult from sustained low horsepower use. Generally speaking, it isdesirable to provide a voltage of about 30-kv. across each spark plug,even when it is fouled to show a shunt resistance as low as 100,000ohms.

The problem is to convert the low D.C. voltage of the battery into avery high voltage pulse. If this is done in a very short period of time,a reduced amount of energy may be employed with each actuating spark,since a rapid build-up of high voltage causes breakdown before there isheavy energy loss in the shunt resistance of the plug. Moreover, it isdesirable to maintain the current through the breaker points low toavoid intolerably rapid deterioration of the points. For example, it isdesirable to provide at the spark plugs a voltage pulse having a risetime of about l to 3 microseconds and having a peak voltage of about30-kv., and at the same time limit the lcurrent through the breakerpoints to about 4 amperes. Moreover, it is desirable to keep the peakvoltage across the breaker points small (no more than about 250 to 350volts), to prevent energy loss in possible arcing in the open breakerpoint air-gap. For the same reason it is desirable to prevent thevoltage across the breaker points from rising too rapidly when they arelirst opened. There vis moreover the problem created by eight cylinderengines of providing less time to store energy from the battery when thebreaker points are closed, than is provide-d with 6 or 4 cylinderengines.

All these factors have combined either to reduce the reliability ofpreviously devised ignition systems, necessitating frequent change ofcomponents with life, or to excessively complicate the mechanism,leading to high initial cost.

It is well known that a voltage pulse may be produced, in an ignitionsystem, by storing energy from the low voltage battery in the magneticiield of an inductor, then transferring the stored energy to a storagecapacitor, and

2,901,670 Patented Aug. 25, 1959 nally discharging the capacitor into adevice such as a transformer to produce the desired voltage pulse. Theoperation involves relatively slow accumulation of energy from thebattery, transfer of the accumulated energy to the storage capacitor,and veryV rapid discharge of the energy so as to produce a voltage pulseof short duration. While systems of this type have been proposedheretofore, such prior systems are not entirely satisfactory for usewith modern high compression engines. The principal reason for this isthe inability of such prior systems to so control the discharge of thestorage capacitor that the discharge invariably takes place when, andonly when, all of the accumulated energy has been transferred to thecapacitor. Since the amplitude of the voltage pulse is dependent uponthe amount of energy discharged from the storage capacitor, the maximumpulse amplitude can be attained in each operating cycle only by insuringthat the discharge of the capacitor will take place when the energystored in the capacitor is a maximum. Prior systems have not providedthis insurance, and when it is considered that the voltage of thebattery may vary and thus cause some variation of the stored energy, itmay be realized that maximum utilization of the stored energy is all themore improtant. Premature -discharge of the storage capacitor may resultin a relatively weak voltage pulse. As far as is known, none of theprior proposed systems have been suciently satisfactory for commercialuse.

Y Accordingly, one object of the present invention is to overcome thedeficiencies of prior systems and to provide an improved ignition systemwhich will give optimum performance of modern automobile engines havingvery high compression ratios.

Another object of this invention is to provide an ignition system, ofthe general character above mentioned, Iin whichprepetitive productionof a very .high voltage pulse is assured. y

Another object of the invention is to provide an ignition system whichwill reliably re wide gap plugs, even though the insulator thereof beconsiderably fouled.

A further object of the invention is to provide an ignition systemenabling increased fuel economy.

A further object of the invention is to provide such a system which issimple in construction and therefore ycapa-ble of low-cost manufacture.

Other objects and features of the invention will be apparent from thedescription to follow.

In accordance with this invention, there is provided a system of thetype above mentioned in which energy is stored in the magnetic field ofanV inductance device and is transferred to a storage capacitor, andthere is further provided in such system a novel arrangement forassuring that the discharge of the capacitor shall take place only whensubstantially all of the accumulated energy has been transferred to thestorage capacitor. More particularly, there is provided an arrangementwhereby the discharge of the storage capacitor is caused to take placein response to reversal of polarity of the voltage across 4an inductor,such reversal taking place only when substantially all of the energy hasbeen transferred to the capacitor. In this way, it is assured thatduring each operating cycle, a voltage pulse Vof maximum amplitude willbe produced.

The preferred embodiment of the invention, as hereinafter described,employs tw'o transformers, one for storage of energy from the batteryand the other for production of the voltage pulse from the discharge ofthe storage capacitor. In such a system, the transformer windings may beself-tuned, i.e., tuned by their respective distributed capacitances, insuch manner as to enhance theV energy transfer Wherever this `is founddesirable, although it is not essential.

.embodiment of the invention; and

Figs. 2 to 4 are explanatory illustrations Yof the'principal voltageswhich are developed at'certain points in the system.

Referring more particularly toV Fig. l, the usual automobile battery isshown at'10 and the usual breaker points are represented at 11, thelatter being shunted by ythe usual condenser 12. The inductance devicefor storing energy from the battery is preferably a transformer 13 whoseprimary winding 14 is in series circuit with the battery and the breakerpoints, although the energystorage device could be a simple inductor.The breaker points serve to recurrently close and open the primarycircuit, thereby to effect recurrent storage of energy in thetransformer. A storage capacitor 15 is connected to the secondarywinding 16 of the transformer to receive energy from the transformerupon each opening of the primary circuit. A unilaterally-conductivedevice 17, preferably in the form of a diode, is connected between thesecondary winding 16 and the capacitor 15, and is poled so as to permitcharging of the capacitor and to prevent discharging thereof into thesecondary winding 16.

Control of the discharge of the storage capacitor 15 is eected by meansof a normally non-conductive device 18, which preferably is an arcdevice and which is serially included in the discharge circuit for thestorage capacitor, the latter circuit also preferably serially includingthe primary winding 19 of an output transformer 20. The arc device 18has two main electrodes 21 and 22, and a starting electrode 23 which isconnected to the lower end of the secondary 16 of transformer 13. Thespacing between electrodes 21 and 22 is such that conduction by device18 can only be initiated by application of a starting voltage to thestarting electrode 23. Such conduction is effected by the reversal ofpolarity of the voltage across secondary 16, which reversal takes placedue to the fact that the secondary winding 16, together with itsdistributed capacitance 24, forms an effective resonant circuit. Whenthe discharge of capacitor 15 takes place, the energy stored therein isquickly transferred through the output transformer to the distributedcapacitance 25 effectively connected across the secondary 26 andresulting from the capacitance of high voltage wiring, the distributor,and the spark plug activated through the distributor.

Considering in greater detail the operation of the system, during theinterval when the breaker points 11 are closed, energy is stored in themagnetic lield of transformer 13 from battery 10 at a relatively slowrate, the current through the breaker points being sufficiently low soas not to cause excessive deterioration of the points. When the breakerpoints open, a positive voltage is applied to the anode of the diode 17,and the diode conducts and effectively closes the charging circuit tothe capacitor 15. At this time there is no appreciable voltage betweenelectrodes 21 and 23 and the arc device 18 is nonconductive. The energystored in transformer 13 is therefore transferred to the storagecapacitor 15 and the latter charges as shown by the rising portion 27 ofthe curve in Fig. 2. Substantially all of the energy that was stored intransformer 13 is transferred to capacitor 15 within approximately 1Acycle of oscillation at the resonant frequency of the elements 15 and16.

During the charging of capacitor 15, the voltage across -the secondarywinding 16 rises, as shown by the rising portion 28 of the curve of Fig.3, the lower end of the winding being positive. When substantially allof the energy has been transferred to capacitor 15, the voltage acrosswinding 16 swings abruptly negative, -asv shown by portion 29 of thecurve of Fig. 3. This is due to the fact that winding 16 and itsdistributed capacitance 24 form an elfective resonant circuit, and thevoltage across the winding oscillates at the resonant frequency of saidcircuit as shown in Fig. 3, although only the solid line portion 29 ofthe curve is of interest here. The voltage swings to a negative peakYsubstantially equal to the original positive peak and cuts olf the diode17, preventing discharge of capacitor 15 into the winding 16. At thesame time, a negative voltage pulse, as shown at 30 in Fig. 4, isapplied between the starting electrode 23 of the arc device 18 and thedischarge electrode 21 thereof, and initiates conduction thereby.

The capacitor 15 now discharges rapidly into the primary 19 oftransformer 20, and the energy that was stored in capacitor 15 istransferred through transformer 20 to the distributed capacitance 25.Consequently a high voltage pulse is developed across distributedcapacitance 25 and causes firing of one of the spark plugs.

As the capacitor 15 discharges, the voltage thereacross decreases asshown by the portion 31 of the curve of Fig. 2. Immediately followingthe full charging (top of line 27 of Fig. 2) of capacitor 15, thebreaker points 11 may close to again store energy in the transformer 13and thus initiate the next operating cycle.

From the foregoing description, it will be seen that maximum amplitudeof the voltage pulse produced by discharge of capacitor 15 is assured,inasmuch as the discharge is not permitted to take place untilsubstantially all of the energy stored in transformer 13 has beentransferred to capacitor 15. `Thus,' during each and every operatingcycle, a very high voltage pulse is supplied to one of the spark plugs.Therefore the system is particularly well adapted for use with modernhigh compression engines and will assure optimum performance of suchengines. Actual tests of the system have proved that it enablesattainment of optimum performance of such engines.

By way of example only, in one physical embodiment of the system thefollowing values are employed.

Primary winding 14 5.5 mh. Secondary winding 16 10 mh. Coeicient ofcoupling of windings 14 and 16 .756.V Capacitor 15..V 2,000micro-microfarads. Primary winding 19 5.7 mh. Secondary winding 26 11mh. Coefiicient of coupling of windings 19 and 26 .6 Distributedcapacitance 25 50 micro-miorofarads.

In the same embodiment a V12-volt battery is employed, a two-ohmresistor is included in series with the battery, a .5 microfaradcondenser is employed across thebreaker points, vand a 1.8 megohmresistor is employed in series with the starting electrode 23 ofthe arcdevice 18' As hereinbefore mentioned, the transformer windings may beself-tuned, if desired, in a manner to enhance energy transfer. Forexample, the secondary of each transformer may be self-tuned to asubharmonic of the frequency to which the primary is self-tuned, so asto obtain an additive effect. In one physical embodiment, the secondaryof transformer 13 was tuned to the seventh subharmonic of the resonantfrequency of the primary, and the secondary of transformer 20 wasself-tuned to the second subharmonic of the resonant frequency of theprimary.

While a preferred embodiment ofthe invention has been illustrated anddescribed, it is to be understood that the invention is not limitedthereto but contemplates such modifications and other embodiments as mayoccur to those skilled in the art.

I claim:

l. In an ignition system, a source of relatively low D.C. voltage, anenergy-storage device including an inductor which together with itsdistributed capacitance 5 :forms an effective resonant circuit having arelatively high resonant frequency, a circuit interconnecting saidsource and said device, means for recurrently closing and opening thellatter circuit to eiect recurrent storage of energy from said source insaid device, a capacitor connected to said inductor for transfer of saidenergy to the capacitor, said inductor and said capacitor forming aresonant circuit having a substantially lower resonant frequency thanthe rst-mentioned resonant circuit, a unilaterally-conductive deviceconnected between said inductor and said capacitor and poled so thattransfer of energy to said capacitor takes place in response to openingof said interconnecting `circuit at a rate determined by the resonantfrequency of said ind-uctor and said capacitor, the iirstmentionedresonant circuit causing abrupt reversal of polarity of the voltageacross said inductor Vwhen substantially all of the energy has beentransferred to said capacitor, a discharge circuit connected to saidcapacitor, an arc device in said discharge circuit connected to thejunction of said unilaterally-conductive device yand said capacitor,said arc device having a starting electrode, means connecting saidstarting electrode to the junction of said inductor and -saidunilaterally-conductive device to initiate discharge of said capacitorin response to the 6 aforementioned labrupt reversal of polarity of thevoltage across said inductor, and means responsive to the discharge ofsaid capacitor for producing a high voltage pulse.

2. An ignition system according to claim 1, wherein said inductancedevice and said means for producing a thigh voltage pulse aretransformers each having selftuned primary and secondary windings, andwherein the secondary wind-ing of each transformer is self-tuned to asubharmonic of the frequency to which the primary winding is self-tunedto enhance the energy transfer therethrough.

References Cited in the le of this patent UNITED STATES PATENTS2,027,617 Randolph Jan. 14, 1936 2,030,228 Randolph et al Feb. 11, 19362,203,579 Randolph June 4, 1940 2,416,971 Welch et al. Mar. 4, 19472,447,377 Tognola et al. Aug. 17, 1948 2,651,005 Tognola Sept. 1, 1953FOREIGN PATENTS 529,558 Great Britain Nov. 22, 1940

